In many dry climates, distributed subterranean plumbing systems are used to supplement natural watering for landscape irrigation. These systems typically consist of one or more zonal fluid circuits each comprising a single control valve, a main supply conduit and a plurality of spray heads connected to the main supply conduit using a threaded adapter commonly called a nipple. In the majority of US residential and commercial ornamental applications, the nipple size is ½″ NPT (National Pipe Thread) and has an internal dimension of approximately 0.55 inches and a minimum length of approximately 1.3 inches when the input and output threads are nearly touching at the midpoint. This shortest length is referred to as a “close nipple.” Longer nipples are also available. The proper length nipple positions the spray head at the desired height for the particular spray head and main supply conduit depth. Adapters are available that allow a close nipple to be extended to any common length, thus making the close nipple a universally adaptable size. When the control valve is open, water flows from the source into the fluid circuit thus pressurizing the main supply conduit. The pressurized water then flows through the plurality of nipple adapters and emanates from the spray heads with velocity sufficient to propel the water through the air. By arranging the location of the spray heads and the direction of spray, large areas can be irrigated with relatively few spray heads.
The spray distance is determined by the elevation angle and velocity of the spray. The elevation angle is typically fixed by the spray head geometry. The velocity is directly related to the pressure in the circuit. The pressure is determined by an equilibrium condition between the supply capacity and the total usage of the spray heads. A problem arises when the equilibrium pressure is insufficient to provide adequate velocity. Inadequate velocity results in insufficient spray distance and thus inadequate water distribution. The inadequate pressure is caused by a mismatch in the system. Too many heads or heads that require high flow volume can over-burden the supply. Alternately, too much restriction or flow distance between the supply and flow heads can compromise the capability of the supply.
Once a distribution problem is recognized, the solution alternatives are very limited. The typical response is to add more heads to the circuit in an attempt to “fill-in” the areas where the existing heads do not adequately irrigate. This often fails to produce the desired results. The additional heads use more flow and thus reduce the equilibrium pressure. This results in additional loss of spray distance and thus introduces new distribution problems. Another alternative is to reduce the number of heads. This allows for higher equilibrium pressure and thus greater spray distance but distribution options are reduced. Two more difficult alternatives are to add a new circuit or improve the plumbing of the existing circuit. Both of these alternatives require digging up the landscape areas that are receiving insufficient irrigation. This fact, combined with high cost and excessive labor requirements, makes these alternatives unattractive.
Prior art has taught that a sequencing valve can be used to allow a fluid flow conduit to be subdivided such that the fluid selectively flows to the subdivided conduits without the need for additional activated control valves. The advantage of these sequencing valves is that a larger number of spray heads can be attached to the subdivided system without causing excessive flow demand.
The first known prior art was Carver, U.S. Pat. No. 2,793,908. Carver taught the method of using a sequencing valve associated with each spray head, said valve being sequenced between open and closed states by application and removal of pressure from the valve inlet port. Carver's valve contained design features which would have made it unreliable in service. The valve depended upon sliding seals that would be subject to wear. Such wear would lead to external leakage. The sliding seals were also in contact with the fluid passing through the valve. It is likely that impurities in the fluid would have caused frictional changes in the seals that would impede proper operation. The Carver valve was also very large compared to the normal flow conduit.
Perlis, U.S. Pat. No. 3,018,788 taught of an improved design that eliminated most of these problems. Perlis' valve was more compact and closely matched the existing conduit size. Perlis' valve also did not rely on sliding seals and avoided any possibility of external leakage due to wear. Perlis' valve had a critical flaw, however, wherein the pressure responsive piston relied upon a close fit within the valve body to prevent the fluid from passing the piston without actuating the valve. This valve would have been very sensitive to impurities such as dirt or grit which would become lodged between the piston and the housing thus rendering the valve non-functional. Perlis' improved valve, U.S. Pat. No. 3,147,770 re-arranged the sequencing and valve means to avoid the aforementioned contamination problem at the expense of increased size and addition of a sliding internal seal.
Henning, et at U.S. Pat. No. 5,609,178 taught of an alternative means to actuate the valve wherein a flow obstruction within the valve caused a differential pressure between the inlet and outlet ports that actuated the sequencing means. This method is undesirable because the design requires a predetermined flow rate to operate properly and necessarily causes a pressure loss as the fluid passes through.
Perhaps the most advanced prior art belongs to Sully et al, U.S. Pat. No. 3,241,569. In this example, the major problems related to sliding seals and contamination are fully eliminated. However, this design still has major shortcomings. It is large and complex and therefore cannot be retrofit into residential systems economically. It also requires the fluid to make two 90 degree turns through a passage that is relatively small compared to the inlet and outlet ports. While this arrangement is widely accepted in the art of flow control valves, it is also well known to cause a relatively large pressure loss when the fluid flow rate through the valve is high compared to the port size.
Other prior art failed to fully address all of the shortcomings described here. Examples include:                Kah, Jr. et al, U.S. Pat. No. 3,519,016        Judd, U.S. Pat. No. 3,853,145        Rosenberg, U.S. Pat. No. 4,116,216 and U.S. Pat. No. 4,221,236        Callison, U.S. Pat. No. 4,632,361 and U.S. Pat. No. 4,662,397        Fischer, U.S. Pat. No. 5,022,426        Young, et al, U.S. Pat. No. 6,622,933        
All of the above referenced patents suffer from one or more of the following shortcomings: (1) The pressure responsive and/or sequencing means is exposed to the fluid flow and is therefore sensitive to impurities in the fluid; (2) The size and/or complexity does not allow for economical retrofit within existing residential systems; and (3) The fluid flow path contains abrupt changes of cross sectional area and/or direction that lead to large pressure losses for high fluid flow rates.